I've been having "issues" which necessitated a visit to the dentist for other-than-cleaning. She (left-handed, lady dentist -- I love her!) educated on some basic facts.
The old, silver-looking material previously used for filling teeth is stronger than the tooth itself. As a matter of physics, the weaker material -- that of the tooth -- will fail first, eventually resulting in cracked teeth requiring crowns.
The new, composite material bonds with the tooth, but will fail more frequently requiring filling replacement; this, however, leaves the tooth itself intact. Additionally, when drilling out the composite, no more tooth material itself needs removal as happens with the silver-type fillings.
It may pay right now, before TSHTF, to have some older, silver fillings replaced while your teeth are still whole.